Sound shell structure



FIG. 1 is a front perspective view of a sound shell structure;

FIG. 2 is a rear perspective view of the structure;

FIG. 3 is a front elevational view of the structure of FIG. 1;

FIG. 4 is a side elevational view of the structure of FIG. 1; and

FIG. 5 is a top plan view of the structure of FIG. 1. 

The ornamental design for a sound shell structure, substantially as shown and described. 